1. Field of the Invention
The present invention relates to a device which is connected to a communication cable for a noise inspection.
2. Description of the Related Art
In a system which performs a communication among a plurality of devices through electric cables, an external noise may affect the electric cables and cause a communication error. When such a communication error occurs, the phenomenon is reproduced in order to inspect a factor at the subject work place, and an occurrence frequency and an occurrence timing are confirmed. Then, a component affected by the external noise is specified by taking actions such as attaching a noise reduction component (for example, a ferrite core) to a cable which seems to be susceptible to the noise to confirm an effect, or separating a cable linked to a device suspected as a noise source from a cable which seems to be susceptible to the noise.
As a conventional technology for specifying such a factor of the communication error, JP 3891237 B2 discloses a communication data monitoring device which is connected to a communication line to analyze a communication according to a communication protocol, determines that an error occurs when a trigger condition is satisfied, and records signal waveform data.
However, in a case where a frequency of the noise is low and a frequency of the communication is not so high, the data communication and the noise timing may not be matched in some cases. In addition, since the communication error does not occur so often, it may take time for reproducing the phenomenon. In such a case, it takes significantly long time for the inspection by the above method.
In addition, in the system not having a method for specifying devices between which an error occurs in the communication, it takes significantly long time to specify a component which is affected by the external noise.
On the other hand, in the technology disclosed in JP 3891237 B2, the cable affected by the noise can be specified by connecting monitor devices to all the communication lines. However, the result is not changed in that it takes time for the inspection.